Relationship between alloy composition, microstructure and exfoliation corrosion in Al–Zn–Mg–Cu alloys

The exfoliation corrosion (EFC) susceptibility of several 7000 Aluminium alloys has been studied after a variety of heat treatments using two independent corrosion tests (standard EXCO test and an electrochemical test based on potential transients analysis), together with detailed microstructural examinations. It is proposed that depending on heat treatment EFC may occur via two different mechanisms: inter-granular dissolution induced damage (IDD) or inter-granular fracture induced damage (IFD). The coexistence of these two mechanisms, leading to EFC, and their relative predominance explain the influence of alloy composition and heat treatment on EFC susceptibility via the confrontation of the two corrosion tests.

► We evaluate the exfoliation corrosion of 7000 series Al alloys with various microstructures.
► We use the EXCO test and an analysis of potential transients during galvanostatic testing.
► Based on microstructure and corrosion morphology, two exfoliation mechanisms are identified.
► It is shown how these two mechanisms depend on alloy content and heat treatment.